The present invention relates to a shaped plastic magnet for use in rotors of compact motors, as well as other applications and a method of making the same.
It is well known that permanent magnets are used in a vast field of applications. They play an especially important role in electronic appliances as a component in compact motors. The performance of permanent magnets has improved year after year. With regard to the magnetic material, there has been a shift from Alnico to ferrite magnets, and further to samarium-cobalt (Smxe2x80x94Co) or neodymium-iron-boron (Ndxe2x80x94Fexe2x80x94B) type magnets, i.e., to those having higher magnetic flux densities.
Formerly, the permanent magnets were used in the form of metallic elements, but it is also well known that they are now used in the form of shaped bodies prepared by sintering compounds, or in the form of resin bonded magnets obtained by molding a kneaded product of magnetic powders with resin powder binders (see, for instance, JP-B-Hei6-87634, wherein the term xe2x80x9cJP-B-xe2x80x9d signifies xe2x80x9can examined published Japanese patent applicationxe2x80x9d).
More recently, SmFeN magnets are being employed as a magnet having a high maximum energy product. These types of magnets are expected to be most suitable for use in the rotors of compact motors embedded in compact instruments such as cameras and watches because, due to their high maximum energy product, they can maintain high flux densities even if they are minimized in size.
However, as is described in detail hereinafter, SmFeN magnets suffer from the presence of unstable Fe (iron) that is incorporated in the bonded magnet because the Fe component accounts for about 67% of the entire material. The iron that is present in an unstable state undergoes corrosion and generates rust which shortens the life of the magnet, and, moreover, the rust deposits as a fine powder on the surface of the magnet during the use of the magnet, thereby impairing the performance of the motor, etc., in which the magnet is incorporated. To cope with the problem of corrosion, it is known to bake coat the magnet with a thermosetting resin such as a fluroresin, a phenolic resin, an epoxy resin, or a modified product thereof. However, there is still a problem that a sufficiently high corrosion resistance is not realized.
As a means to overcome the problems above, the shaped plastic magnet according to the present invention provides a shaped plastic magnet comprising a shaped body obtained by molding a mixture of an SmFeN magnetic powder with a resin binder into a desired shape, where the surface of the molded shaped body is subjected to a coating treatment using a phosphate. In this manner, the Fe component that is present in the surface of the bonded magnet provides a phosphate compound having excellent corrosion resistance and high adhesiveness.